The present invention relates to electronic ultrasonic sounding for exploring a piece of body to be examined, particularly although not exclusively in depth, i.e. in B echography or B scan.
Inventor's U.S. Pat. No. 4,119,938 and French Pat. No. 2,292,978 disclose and claim an ultrasonic imaging device comprising N elementary transducers distributed at equal intervals along a displacement line and capable of operating at ultrasonic frequency f, a generator (or receiver) associated with the transducers by dephasing means, and means for storing the distribution over n successive elementary transducers (n being an integer less than N) of the phases corresponding to focusing at a given distance from the line for frequency f. Switching means connect a group of n transducers to the dephasing means and to the generator (or receiver) in accordance with said distribution. Then the group of n elementary transducers is shifted along said line at equal time intervals. The dephasing means are provided for giving phase shifts which are multiples of 2.pi./a (a being an integer less than n) and said storage means store the distribution of the phase shifts.
The device of that type described by way of example in French Pat. No. 2 292 978 uses the same number n of successive elementary transducers for reception and emission, with the same distribution, corresponding to several Fresnel zones associated with focusing at a desired distance and phase sampling uses two phases which differ from each other by .pi.. The patent specification also contemplates a finer sampling, by using a number a of phases greater than 2. But it is then necessary to provide more complex switching means and emission and reception circuits ensuring phase shifts which are multiples of 2.pi./a.
Another prior art device (U.S. Pat. No. 4,117,446) includes memory means and registers having a number of binary positions p times greater than that used in the device described in U.S. Pat. No. 4,119,938 and may provide a first Fresnel configuration of "lens" at emission-transmission and p-1 Fresnel configurations or "lenses" at reception, having different apertures and focal lengths. Switching of the latter lenses may be rapid enough to have optimum dynamic focusing. The term "dynamic focusing" designates a modification by jumps of the focal distance progressively as the echoes return so that at any moment the receiver configuration is optimum for receiving the echoes liable to be formed at the position occupied at the same time by an ultrasonic return echo.
In a particular embodiment described in U.S. Pat. No. 4,117,446, binary quantization of the phase is used, a quantization which has the merit of simplicity. For reducing the secondary lobes to an acceptable level, the emitting lens comprises a number n.sub.0 of transducers less than the number n used at reception and corresponding to the first Fresnel zone only. As a counterpart, there is an attendant disadvantage: the resolution is decreased.
It is an object of the invention to improve upon the prior art techniques of ultrasonic examination and imaging, particularly, in that fine phase sampling is achieved with simple and relatively low cost means; it is another object to provide improved focusing upon transmission as well as upon reception without secondary lobes of a prohibitive level.
According to an aspect of the invention, there is provided a device for ultrasonic imaging, comprising: n elementary transducers distributed at equal intervals along a predetermined line and operable at ultrasonic frequency f; a generator of electrical pulses; and time delay means operatively associated with said generator for delivering, in response to each electrical pulse from said generator, a plurality of low level pulses delayed by increased time delays .tau., . . . , (a-1).tau., (.tau. being a predetermined time delay) on different channels, a being an integer less than n. Means are provided for storing a distribution of said a time delays between said n transducers corresponding to focusing of transmitted ultrasonic energy at a point located at a predetermined distance from said line at frequency f. A plurality of amplifiers are each associated with an individual one of said transducers for delivering an energizing pulse to the associated transducer in response to one of said low level pulses appearing on an associated channel selected by the storing means.
Since the lines and the means for controlling the amplifiers have not to transmit the power necessary for energizing the transducers (which is supplied by the amplifiers), the amplifiers may be controlled by analog multiplexers, which now exist in the form of inexpensive integrated circuits.
According to another aspect of the invention, the switching means may comprise, for each transducer, a supply amplifier and a multiplexer for controlling the amplifier by means of a low-level signal coming from one of the a lines or channels of a general bus. Each line or channel receives R pulse signal from the emitter (transmitter) through means giving relative delays which are multiples of 2.pi./a.
According to a further aspect of the invention, which relates to reception rather than transmission, a multiplexer (which will typically be used also at transmission) is associated with each transducer and is connected, through a common bus, to a channels on which phase-shift means are located. A circuit is provided for summing the analog reception echoed signals. Each multiplexer may comprise a multi-bit control input connected to a respective stage of a shift register associated with a clock for moving said stored distribution along the register, whereby electronic scanning may be achieved if the n transducers which are simultaneously in operation are part only of a greater number N of transducers evenly distributed along a scanning line.
This arrangement provides the advantages already mentioned in U.S. Pat. No. 4,117,446, however in combination with a much improved fine sampling favorable to a very high resolution.
Practically, a resolution close to the maximum is reached by using modulo 2.pi./8 sampling of the phase; it requires a bus line having eight channels associated with the multiplexers. The same multiplexers convey, in one direction, the signals for controlling the amplifiers (logic control at a 5 volt level for example) and, in the other direction, the reception signals provided by the transducers and brought up to a suitable level by means of a linear amplifier.
According to yet another aspect of the invention, there is provided an electronic translation ultrasonic sounding device comprising N elementary transducers distributed at equal intervals along a translation line and capable of operating at an ultrasonic frequency f, a generator (or receiver) associated with the transducers by phase-shift means, and means for storing the distribution over n elementary transducers (n being less than N) of the phases corresponding to focusing at a given distance from the line for frequency f, as well as switching means for connecting a group of n transducers to the phase-shift means and to the generator (or receiver) depending on said distribution, then in shifting at equal intervals of time, the group of n elementary transducers along said line. The phase-shift means are provided for giving a different phase shifts and the storage means for storing the distribution of the a phase shifts between the n transducers. The switching means comprise, for each transducer, a supply amplifier and a multiplexer for controlling the amplifier by means of a low-level signal coming from one of the a channels of a general bus line, these channels being each associated with one of the phase-shift means.
The a phase shifts may be distributed evenly; but in some cases it is more advantageous to have different intervals, for example to take into account the variation of the slope of the representative curve of the phase depending on the distance to the center of the group of n transducers. The phase-shift means may themselves be formed by very different elements, such as phase-shifters, delay lines and, at emission, shift registers.
To ensure dynamic focusing, it is sufficient to control the multiplexers, not only at emission but also for the p-1 successive reception periods, by means of N outputs from a register which transit words of b bits on pN positions, the word b causing, for a first value, blocking of the multiplexer (transducer not supplied) and, for the others, opening of the multiplexer with selection of one of the a channels of the bus line.
An additional result sought by the invention in the case of dynamic focusing consists in minimizing the extent of the switching noise engendered during focal distance changes, which noise risks being greater than the weak echoes received, without introducing any frame disturbance harmful to the quality of the image.
To this end, the invention provides a device which alternates two groups of complementary focal zones.
The invention will be better understood from reading the description which follows of devices which form particular embodiments thereof, given by way of nonlimiting examples.